A Tail of Murder
by jedi-from-mordor
Summary: Post series finale minus epilogue. Captain Kate Beckett is back at work, just in time for a very odd corpse to show up. The investigation leads to an ancient secret...
1. Chapter 1

**A Tail of Murder**

1

A knock on the door interrupted Kate Beckett from her paperwork. "Come in," she called and looked up.

Detective Ryan stepped in. "We've got a body, Captain. Odd one, too."

"Sure," she said, reaching for her coat. "Since when do you knock?"

"Since I interrupted you and Castle last month," he said and blushed.

So did she. "I didn't even notice," she shuddered. "Do you think Castle did?"

"Did what?" the said writer interrupted. "You going somewhere?"

"_We're_ going to a crime scene," Kate said.

He smiled and handed Beckett a cup of coffee. "Decaf?" she asked.

"You've had your daily permitted dose." His eyes dropped to her stomach. Either she was starting to show, or his imagination was playing tricks on him. "How's my youngest daughter?"

"Wait–you know it's a girl?" Ryan demanded.

"No," Beckett said in frustration. "It's a Castle hunch–meaning he pulled it out his–"

"Hey–my hunches are why you keep me around!"

"Not only," Beckett clasped his hand in hers. "Not only."

* * *

At the scene, they met almost twenty frustrated people and Detective Esposito. "Morning, Espo. What happened?"

"City finally granted the lot owner permission for demolition of this warehouse," the other detective said. "He called in the construction crew, and they found–well, take a look."

They entered and approached Lanie, who was crouching at the corner. "Hey, Lanie."

"Hi, guys. Look at this."

"Oh, my god!" Kate exclaimed when Lanie pulled away the tarp.

"Is that a mummy?" Castle asked.

"It's desiccated like one," Lanie informed them. "That will make TOD hard to establish."

"Yeah," Castle quipped. "He could be thousands of years old."

"Doubtful," Lanie retorted. "It's a she, by the way."

"Why can't she be thousands of years old?" Castle almost whined.

"Because of this," Lanie turned the dead woman's neck to show them the hole in the back of the head. "And here's the bullet." She handed them a sealed evidence back.

"Single shot?"

Lanie nodded.

"Not a pistol one, either. Rifle or carbine," Esposito said. "Don't see a lot of those in the city."

"But why the mummy?"

"I don't know if it's technically a mummy. The body was dried out post-mortem."

"How?" Beckett asked.

"Why?" Castle added.

Lanie shrugged. "CSU says no sign of fire in the building. Either it was done elsewhere or they used electric heaters."

"How long would it take?"

"Several hours," Lanie said. "The husk is thirty-two pounds. Since our bodies are about seventy percent water, it'd estimate eight to nine hours for the desiccation."

"So the latest it could have happened was last night–two to three AM. Earliest–"

"Could be years."

"ID?"

"None. No clothes, either."

"Sexual assault?"

"Evidence would dry out with everything else."

"Not if our killer had a fetish for dry-humping."

"Eew, Castle," Beckett said, but then nodded. "Check anyway."

She turned to her detectives. "Have uniforms canvass the area for witnesses last night. Espo, talk to the owner and crew–find when was the last time anyone was in the building. Castle? Do you have an idea?"

"What did she look like?"

"Huh?" Lanie and Esposito said in unison.

"Can we go from that–" he pointed at the husk, "–and reconstruct what she looked like when she was alive?"

Lanie considered. "It's not my field of expertise, but there are people who do that sort of work. Think it's worth it?"

"We don't have any other way to ID our vic," Beckett said. "Do it."

Castle hesitated for a while, staring at the mummy. "You okay, babe?"

He nodded. "Something doesn't add up."

"It's weird," Beckett admitted, "but we've seen stranger."

"No–there's literally something that–"

"What is it?"

"She's missing a finger."

"I know. I noted that in my report," Lanie said. "So?"

"Isn't it obvious? She was killed for her ring."

* * *

Two days later, they made no real progress in the case. Castle tried to use his connections to see if any unusual rings had been sold since the murder, but depending on your criteria of _unusual_, you got either nothing or too much.

Beckett's iPad chirped. "What is it?"

"Forensic anthropology," she answered, heading to the murder board. "According to…" she read the message, "… Dr. Shalon, our vic looked like this."

The image was of a Caucasian woman with a narrow face, tall forehead, and thin nose. The electronic image permitted switching out hair styles and colors–that was still unknown.

"Alright. Vikram, can you run this through facial recognition databases?"

The tech nodded. "She looks a bit creepy," he said.

"I was thinking the same thing."

"Really? Creepy? I think you're just projecting how we found her."

"Hit!" Vikram announced.

"Where?" Beckett demanded.

"Here. Look familiar?"

It wasn't a photo, but a police sketch. The hair in this one was shoulder length, straight, and black, the eyes hazel–but the facial features were unmistakably a match to the reconstruction.

"Who is it?"

Ryan, who had already looked up the case, shook his head in bemusement. "Three days ago, the 26th precinct arrested a woman in Brooklyn for public nudity. She told them this one–our Jane Doe–stole her clothes when she was walking on the beach."

"I understand revenge for that, but isn't murder going a bit far?"

"We should still talk to her. Come on, Castle. Let's see what we can uncover."

"Seriously?" Both Vikram and Ryan stared at Beckett. Castle, on the other hand, looked quite proud. "Why, I believe I'm finally rubbing off on you, Beckett."

Kate tried to glare, but it transformed into a yawn without warning. "Your kid is making me tired, Castle. You're driving–and no, you're not allowed to use the siren."

* * *

"Janice Ruthers!" Kate called, knocking on the door.

The resident opened it. "Who are you?" she demanded.

Kate flashed her badge. "NYPD."

Janice's face turned angry. "What more do you want–I paid the fucking fine–leave–"

Castle held the door she was about to slam. "I don't care about indecent exposure," Kate said. "Your clothes thief was found dead–"

Janice's eyes flew wide open. "Oh, my God!"

"Can we talk? We're trying to piece together her activities."

"Well, I only saw her that once–you can bet I would have gone for her if I saw–"

"Castle?" Beckett interrupted the witness.

"Ms. Ruthers," Castle said casually, "is it possible _you_ were the intended victim and the killer made a mistake because–"

"What–me? Who goes after a hairdresser?"

"It's possible," Beckett admitted. "Anything unusual recently–unhappy clients, personal troubles, threatening calls?"

"No."

"Can you give us the details of your encounter?"

"I already did–do you even know who she is–uhm, was?"

"You're the only one so far with even a hint of motive–"

"What motive–you don't think I did it?"

"Well, did you?" Castle asked point-blank.

"Of course not!"

"You just said you would have confronted her–"

"Well–yeah–I mean, who does something this crazy? But I wouldn't have _killed_ her! Besides, I lived the last two days surrounded by cops trying to settle this indecent exposure shit."

"Did you give them a list of what was stolen with the clothes? Phone, credit cards–?"

"Yeah, but it won't help. I already got the phone." Janice picked up her cell from the kitchen table and showed them. "Call and text history I sent to the bitch is still there."

"You traced it."

"By the time I was with the cops, she ditched it. We found it in a trash bin on 9th Avenue."

"When?" Kate asked.

"Wednesday–about 11."

"Haven't traced any movement?"

"Nope."

"And credit cards?"

"Cancelled all of them–but there's nothing. She knew what she was doing, then," Castle said.

"But why steal clothes?"

Janice smiled. "Haven't you read what I told the other cops? _She_ was naked before she robbed me."

* * *

"A woman walks about naked but doesn't get noticed. She steals clothes from another, and is killed within three days–and on top of that, gets dried out to a husk. Something doesn't add up."

"Try nothing adds up."

"Secret society of nudists trying to take over the world–okay the attack on Ruthers doesn't fit that."

"We found something, guys," Ryan and Vikram approached the murder board.

"Yeah? What?"

"Surveillance footage," Ryan said. "This," he posted a photo on the board, "is at the intersection of 12th and Jefferson. This one," he tacked up another, "is from the B Line station nearby. Our warehouse is between the two locations."

Both photos showed a young woman, blonde, curly haired, dressed in jeans and a tank top. "So?" Beckett said. "Probably hundreds of people walked past."

"It's the evening before the body was found–and she didn't just walk. Not unless she's the slowest walker in New York. These photos are nearly five hours apart, and she wasn't seen anywhere else within that time."

Beckett considered. "It's not enough to get an arrest warrant, but we can talk to her. Can you find out who she is?"

"Already did, Captain," Vikram announced. "Got a hit pretty quick, too. You'll like this," he glanced at Castle. "She's an author."

Castle sprang up. "Really? I don't recognize her."

"Not your specialty, Castle," Ryan said with a smile. "She writes nonfiction." He put up a final picture, printed out from a website. "Meet amateur marine biologist from Australia named Rikki Chadwick."


	2. Chapter 2

The lecture hall erupted in applause as Chadwick concluded her presentation. "Up next," the announcer said, "Dr. Viktor Salliger, presenting new findings of marine life using shipwrecks on the North Atlantic Seafloor."

"You know, this is fascinating," Castle whispered, studying posters and photographs all around the hall.

"Try nightmare inducing."

"Nonsense," Castle declared, and rubbed her stomach. "Don't listen to your mother, sweetie. You'll love trips to the aquarium with Daddy, just like your big sister."

Kate barely managed a straight face. "I suppose not seeing the appeal made me a strange girl." She sighed and turned serious as she approached the stage.

Rikki Chadwick looked impossibly young to Rick, barely older than Alexis. "Miss Chadwick," Kate approached and flashed her badge. "NYPD. We'd like to ask you a few questions."

"Uhm… alright," she said with a note of hesitation. "What's going on?"

"Where were you Thursday evening between nine PM and two AM?"

"Bar on Upper Westside," she answered. "I had just flown in, didn't feel like sleeping. Still on home time."

"Name of the bar?" Kate persisted.

"Can't recall–"

Beckett whipped out the surveillance photos. "These say you haven't stayed at the bar all night. Not exactly a tourist area. What were you doing–"

A fire alarm echoed in the auditorium. Instinctively, both Castle and Beckett turned their heads, and in that moment, Chadwick jumped up and fled. "Hey!" Castle shouted and ran after her.

"Stop! NYPD!" Beckett drew her gun and ran after the other woman. But Chadwick clearly knew the building better than either of them. Kate took out her radio. "Ryan, Espo," she summoned their backup. "Chadwick fled. We're in pursuit."

"Got it. Careful, captain."

"I don't think she's armed, but who knows."

When they exited the building, she'd met disgruntled Ryan and Esposito, and Castle in the annoyingly good mood he put on when things got _weird_.

"You're not going to believe this, Beckett," he declared.

"You lost her."

"Yeah," Ryan sighed. "She jumped into the river."

Kate raised her eyebrows. "Really?"

"Really. And disappeared."

"How–I mean, it's been a few minutes."

"Haven't seen anything."

"Should we call in a diving team?" Esposito suggested.

"Not yet."

"Pointless, probably," Castle said.

"Why?" Ryan asked.

"You saw her. She didn't hesitate to dive in. By the way, there's at least thirty feet from the parapet to the water here. Unless you're an Olympic diver, you'd hesitate from that alone–but she just jumped. I'd wager she knew what she'd do once in the water, as well."

Esposito looked skeptical. "I've heard of getaway cars, getaway boats, getaway planes–are you suggesting a getaway submarine?"

"Hey–that's a great idea!"

"A very unlikely one," Beckett brought them back. "Coast Guard has been patrolling the harbor constantly since 9/11. Sneaking in a submarine…"

"So what do we do?"

"Put out an APB on Chadwick. Find that bar–talk to the patrons, see if they remember when she left. Get a warrant and search her hotel room."

"Excuse me, Captain."

"Yes?" she turned to see an African-American man in a firefighter's uniform.

"Lieutenant Hutchninson. You were in the auditorium when the fire started?"

"Yes–wait. You mean there actually was a fire? Not someone pulling the alarm?"

"No, Captain. We put it out, and are trying to find the cause. We're in a bit of a loss."

"Join the club," Esposito muttered.

"We were hoping you may have seen something."

"Sorry. My attention was on our suspect who used the chaos to make a run. I guessed she had an accomplice pull it."

Hutchinson shook his head. "No accomplice. The fire was absolutely real."

"Hang on," Castle said. "I remember something odd."

"What?"

"Chadwick. Right before the alarm–she did a sort of twitch with her wrist." He demonstrated a gesture. "It's not a habit–she only did it that one time, _very_ deliberately."

"Remote trigger?" Hutchinson considered.

"I was thinking more of harnessing the elemental power," Castle replied.

"Is he serious?"

"He's my husband. I plead the fifth." Kate's body suppressed a grin.

"Elemental powers or not, Miss Chadwick is involved." She handed Hutchinson her card. "Let me know fi you find something that might lead us to her."

Hutchinson nodded and gave her his own card. "You catch her, I'd like to speak. Something about his fire doesn't sit right with me."

"No problem, Lieutenant. Castle?"

"Yeah?" he said. "You okay?"

"I… I'm sorry."

"For what?"

"I ran after her. And yeah, she was probably unarmed, but the point is–my cop instincts overrode my mothering. I–"

He pulled her in and held her. "I hadn't thought to warn you off, either."

"It's my responsibility."

"No," he declared. "It's ours."

"He's inside me."

"_She_. And that doesn't matter. She's our responsibility. We're partners."

"Always."

"Besides," he continued, "Tune up that excellent cop instinct and tell me–do you really think Chadwick did it?"

Kate shook her head. "No. She just was caught unawares and ran the best way she knew. The diving skill is easy to explain with her line of work. But she is connected, or she wouldn't have run in the first place.

"We'll find her," Ryan assured them. "It' snot like she can flee the country by swimming."

"Getaway submarine," Castle murmured, but was met with glares from the cops.

* * *

"Hey, Castles," Ryan greeted them the next morning. He was smiling."

"Good news?" Beckett asked.

"After we searched Chadwick's hotel room, we went through her laptop. She had a ton of papers by Dr. Larry Hong."

"Who's that?"

"Marine archaeologist. He's speaking at the same conference, so Espo and I are heading out to talk to him."

"A bit of a stretch, but alright."

"You don't want us to come along? In case he is using the submarine?"

Esposito glared and met Beckett's eyes. "Nah… you can interrogate Chadwick."

"We got her?"

"MTA police caught her on the Upper Westside this morning. They're bringing her in now."

"No incidents?"

"By the book, Captain."

"Alright, thanks." They turned to the elevator, where several uniformed officers were escorting cuffed and disheveled-looking Rikki Chadwick. the moment she saw Beckett and Castle, her face turned from calmness to frustration.

* * *

Castle went to fix her a cup of coffee, so Beckett began the interrogation by herself. Chadwick sat, quickly tapping her fingers together as best as the cuffs allowed. Kate suppressed a sigh. Talkative suspects were a lot easier to work. She'd have to open this one.

"Do you know this woman?" she asked and lay down the sketch produced from Janice Ruthers' description.

Chadwick tried to keep control of her face, but couldn't quite manage. "I see you do," Kate barreled on. "Did you kill her?"

"What? No–she's dead?"

"That's right. And you've been caught on cameras next to where her body was found." One again, Beckett showed the surveillance photos. "Hell of a coincidence. Explain yourself."

Castle walked in at that point, holding Beckett's coffee. Kate turned to take it, but paused when her ears registered a barely audible click.

"Kate, look out!" Castle shouted and shoved her out of the way as Chadwick, somehow free, had raised her hand, which was emitting a strange white light.

In the process of pushing her, Castle dropped the coffee mug, which rolled across the table and into Chadwick's lap, where it spilled open.

"Ow!" Chadwick shouted in pain, and then, her face turning to horror, "NO!"

"Hands up!" Beckett shouted, gun out and trained on Chadwick.

She did so… and in a flash of light, fell from the chair. Kate rose, gestured for Castle to stay behind, and walked around the table.

Chadwick lay on the floor, face buried in her hands. Instead of a green jacket and t-shirt, she wore a glittering orange bikini tightly molded to he body. And that change was by far the least strange one that occurred.

Below the waste, she no longer had legs. Instead, she boasted a scaly fish tail in the same orange tone as the bikini top. The tail made her two feet taller–or was it longer?

"Castle, please tell me this is a pregnancy-induced hallucination."

His reply was to pinch her ass. "Ouch–what was that for?"

"Not a dream, then. I give you permission to do the same."

"Later." She took several deep breaths. "It's real, then?"

"Yes, Beckett. Our suspect is a mermaid."


	3. Chapter 3

3

"Can you turn back?" Kate asked Chadwick. The mermaid looked up in sheer terror. "What?" she asked.

"Back to… human form?" Kate suggested. "Is that even the right term?"

"Yeah–it is. And yes, I can," Chadwick answered. "I just need to dry myself."

Castle started removing his jacket, but, she halted him. "No need." She put her hand over her tail, crunched her face in concentration, and steam started pouring off the scales. The air in the interrogation room turned considerably warmer.

"You make heat?" Castle asked in surprise.

"It's a mermaid power–well, it's _my_ mermaid power," she answered before another flash of light filled the room. When it subsided, Chadwick had her legs back. Castle helped her up.

"You set the fire in the auditorium," he said.

"I did," she admitted. "I panicked when you showed me those photos. Like I did here." She shook her head ruefully. "And it backfired."

"The coffee did it?"

"Any water on my body, and if I don't dry it–ten seconds later, I got the tail."

"How can you live?"

Chadwick shrugged. "Got used to it, I guess. I was fifteen when I got the powers."

"I'm sure you were thrilled."

She shrugged. "Still am. Why do you think I do what I do?"

"And what is that you do, Miss Chadwick?" Beckett turned the conversation. "Specifically–what happened between those two photos?"

Chadwick took a long time to think. "I really don't want more people to know about mermaids. But I need help–clearly this has gotten out of control."

"Did you kill this woman?" Beckett pointed to the sketch and to the forensic reconstruction.

"No."

"Do you know who she was?"

"Yes."

"Was she a mermaid?" Castle guessed.

"She was–but not like me. She was born a mermaid. That's why she had to steal that poor beachgoers clothes. She was all alone in the city."

"But you've met."

Chadwick nodded. "I was the one who told her to throw away the cell phone, to avoid tracking."

"So you met Monday morning. And then–"

"Not until she was already dead. I found her body in the warehouse."

"And what did you do?"

"First–dried it out." She flexed her hands. "Blood gave her the tail, but then she turned back. And I just kept drying until–"

"You had a mummy."

"I was going to make a plan to get rid of it later. To keep the mermaids' secret. I didn't count on anyone going there anytime soon."

"Neither did the killer, apparently."

"Why–"

"Wait–can I ask for something, Detective?"

Kate looked at her. "Depends on what it is."

"You know my biggest secret already. I'll tell you everything–I'll be more than willing to tell you everything if it brings Romida's murderer to justice."

"Romida? That was her name?"

"Yes. Just–_not here_. It's a long story, and I don't want to be overheard. So somewhere secluded. Please."

Beckett considered it. "I'm going to insist on a lockjack," she said. "And with your… unique situation, I can't put it on your ankle. It'll have to be arm or neck."

Chadwick shrugged. "Fine. Now, as to the secluded location?"

"How about our place in the Hamptons?"

Beckett blinked. "That's actually a good idea. "We'll arrange this and talk to you tonight."

When the mermaid left under escort, she turned to her husband. "I guess even after two years, it still hasn't sunk in my mind that it's _our_ place in the Hamptons."

"It's been yours for a lot longer than that."

She put her arm around him. "We've got some good memories there. First vacation together, the wedding…"

"The medical leave after Locksat."

"That wasn't so good."

"The recovery was. And now we get to talk to a mermaid. Hey–it's our fairytale place."

Beckett only laughed.

* * *

Kate leaned back into her husband, dug her feet in the sand, and watched curiously as Chadwick lifted her hand towards the water. The light emanating from her ring resembled that of the moon. She'd told them it was a mermaid status symbol, as well as a tool of power, and had confirmed that Romida, their victim, had one as well.

"Got it," she said, and picked up a dry towel. "She's here."

"She–"

A woman's head emerged from the water where the light from Chadwick's ring shone, and the newcomer let the wave carry her forward. When the water receded, it revealed the scaly tail terminating her body. Chadwick ran up, wrapped the towel around her, and quickly dried her up. The tail sparked, got obscured, and transformed into a pair of legs.

"Kick me. Hi. I'm Captain Beckett," she said.

"Rita Santos," the new mermaid shook her head. She appeared about her age and spoke in an Australian accent. "So one of us was killed on land. Very unusual."

"Let's go inside," Chadwick said.

"I better start getting answers," Kate muttered.

"Answers can be dangerous," Santos replied, but she smiled as she said it.

"Don't we know it," Castle said.

* * *

"Explorers of the sea, whether human or mermaid," Chadwick said in a manner of delivering a lecture, "are usually interested in either ocean life or sunken artifacts. I'm the former, but I keep an eye on the latter. Sometimes our interests intersect. In the course of my travels, I found a number of interesting treasures."

She tapped a few keys on her laptop, displaying photos. "I usually left them on the seafloor–safer than any vault on land, or so I thought."

"That's a mermaid one," Santos said, pointing to a silver statuette of a snake.

"I guessed it was–for one thing, it depicts a deep ocean species, unlikely to be encountered by any ancient humans. But in the past few months, some artifacts I found previously vanished."

"Many people dive for treasure here," Castle said.

"The key word is _here_, Mr. Castle," Chadwick said. "So far all the disappeared trinkets were from the North Atlantic. The Pacific is safe. So is everything south of the Azores."

"A pattern," Kate considered. She reached for a notebook and jotted something down. "Why do you think that is?"

"Could it be the fact that you found them?" Santos asked.

"No. Like I said, not my speciality–I don't talk about them in lectures."

"But you keep records–photos," Castle pointed to the computer.

"Hackers? I thought so too, but I had my laptop checked. It's clean. Even in the North Atlantic, not everything I found vanished, and some of these things were pretty close to those that did. This is someone running an independent search."

"Like Castle said–it's not uncommon. Lots of sinkings in the centuries of voyages."

Castle's eyes suddenly widened. "Oh, my god–did you go look at the _Titanic_?"

"I have," Chadwick replied. "It's _interesting_."

"Focus, Castle," Kate said. "Why the suspicion?"

"Because none of these finds have been announced. I said I keep an eye on the specialized publications–well, they aren't there."

"Some people just want money, not scientific results."

Chadwick gave a grim smile. "And that's where it gets suspicious. These are wrecks kilometers deep. You can't dive them with a yacht an an aqualung. You need real deep-sea submersibles. It's almost certain to cost more than the treasure is worth–at least, the artifacts I know about are."

Kate exchanged a look with her husband, who was thinking intensely. "You need submersibles," he drawled carefully.

"Or you need a mermaid," they said together."

Rita looked skeptical. "But why? I've never heard of a mermaid who aspired for human wealth."

"Real mermaid," Rikki muttered.

"What?"

"I tried to talk to the North Atlantic Pod councils. They wouldn't listen. I'm not a real mermaid." She sounded bitterly resigned.

"Why did Romida come to land?"

"She was looking for her daughter."

"What?!"

"Her daughter. She said she needed to find–she was very vague on details, even with me."

Rita shook her head. "No way. Children are absolutely sacred. If a girl just disappeared, Pods from here to Madagascar would be on alert."

"If they knew," Beckett said.

"How would they not?"

"Romida was looking by herself. That sounds unusual for you."

"It is," Rita admitted. "Certainly for Romida."

"Right. So what if she never told her pod?"

"Why not?"

"Hostage."

"What? Castle–"

"Someone took her daughter hostage. He's threatening to kill her unless…" His eyes expanded. "Unless she retrieves treasure for him."

The two mermaids considered this. "Look, this morning, 'possible' in my head definitely excluded the existence of mermaids. You're the experts here. Rule out the possibilities."

"It's not impossible. Though it's very hard to capture a mermaid, even a young girl, at sea. and considering how inexperienced Romida was, I doubt her daughter would have ever ventured on land, either."

"But it could happen. So what will our mermaidnapper do now that he killed the mother?"

Kate nodded. "He'll look for a replacement."

"Take another girl to make the mother enrich him."

"Yeah, but how do we prove it?"

"And how do we catch him out there?"

"Rikki," Rita instructed, "you stay here and advise them. Study recently sold recovered treasures."

The younger mermaid shrugged. "Sure. You're going somewhere?"

"Yeah." They followed her back to the beach. "I'm going to knock some sense into the Pod councils." She smiled at Rikki. "After all, I'm a _real_ mermaid."

"Thanks for your help. I'll be back in a few days."

She shook Castle and Beckett's hands, hugged Rikki, and ran to the water, leaping in headfirst and disappearing under the waves.

"So cool!" Castle whispered, and then turned to his wife. "I wonder what you'd look like with a tail?"


	4. Chapter 4

4

"Well, that line is closed," Ryan said. "Sorry, Beckett. Everyone caught in any surveillance camera in the area alibied out. There are plenty of ways someone could get in there–coverage is distinctly on the sparse side."

"Damn it," Kate considered. Having agreed to keep the existence of mermaids a secret, she was now forced to keep leads away from her team. Not that right now, that looked any more promising.

Her phone rang. "Beckett."

"Hey, Kate," Alexis said. "Can you come to the PI's office? I've called Dad, too. He's on the way."

"What happened?"

"Nothing wrong–just there are two people here claiming they're working with you and they wont' explain their issue to me."

"Rikki Chadwick and Rita Santos?"

"Yeah–"

"I'll be there."

"Rita looks hurt."

"Okay. Thanks, Alexis."

By the time she arrived, Castle was already there, talking with the Australian mermaid. "Oh, my God!" Kate exclaimed. Alexis hadn't been kidding. Rita had a bloody slice across her face, as if slashed by a sword–very recently.

She waved off. "I'm handling it," she said. "Not the first mermaid, not the last."

"But you said it'll remain forever," Chadwick insisted.

"Less prominent," she agreed. "But if it helps us catch this guy, it'll be worth it."

"You found something?"

"We did," Rikki said.

"You hit it pretty much on the head, Mr. Castle. "Somebody's been kidnapping mermaid girls from Atlantic Pods and blackmailing their mothers into treasure hunting. Guy's clever. Each pod, each mother thought it was just her."

"But they told you?" Kate asked.

"No. But I followed one of them when she would meet him."

"You saw him?"

"Rikki?"

The other mermaid plugged her computer to the office TV and showed several photographs. "These I found a few months back on a wreck of the ship called _Fortitude_. It's in the Caribbean," she explained. "And here," she showed several online auction records, "are these things being sold. Anonymously, of course."

"One's missing."

"It is," Rikki confirmed. "We're dealing with a serious problem."

"What is that thing?" Castle asked. "The object was an intricately carved bronze pipe, wider at one end, with opening petals. In the photo it appeared next to a clownfish, so Kate could estimate its length to about a foot.

"I had no idea–believe me, if I did, I'd have either taken it or hid it very, very well when I saw it. I went back yesterday, just in case it was _still_ there. It wasn't. That's when I hurried to find Rita."

"But what is it?"

"It's called the Horn of Alexander, though I think the creator just used that to make it look like Alexander the Great had something to do with it. That's what Ondina told me, at least. It's an anti-mermaid weapon. With the right power source, you can paralyze one."

"What do you mean by the right power source?"

"This," Rikki held up her hand and showed them the ring with an aquamarine stone. "A mermaid's moon ring. That's why it hasn't been widely used. You sort of need it to function to make it function."

"But whoever took it got lucky and now he can take anything he pleases." Rita placed her own hand on the table. The ring finger was covered in a tight bandage. "He ripped it off."

"And your face?"

"Cut it before leaving, hoping blood would attract sharks. Rikki got there first."

"You're welcome."

"I'm sorry this happened to you, but I don't see how it helps us get closer. Did you see him? His face?"

"No. He was in a mask and scuba gear."

"Then what can we do?"

"We know where and when it happened," Rikki said. "Your daughter was most helpful. She searched for ships that were in the area."

The younger mermaid presented a map criss-crossed by multicolored lines. "The closest one was this yacht–the _Cormorant_. Homeport right here in New York. And guess who the owner is?" She gave bitter growl and tapped a key with a jerk, popping out a large photo. "Dr. Viktor Salliger. My mentor."

* * *

"I'm sorry, Dr. Salliger."

"Really?" the man snarled. "Accuse me of murder and now you're sorry?"

"And you don't know who could have taken your yacht?"

"I already told you I had no idea it was even gone."

"That better be so," Ryan interjected.

"You found something?"

"We looked into persons connected to Dr. Salliger. And guess what we found?" Ryan drew to pieces of paper from a manila folder. "One," he said. "David Salliger, your younger brother, owns a carbine. Fires bullets exactly like the one we dug from Jane Doe's skull. Two," he laid out a photograph. "Taken five minutes ago. "Your brother has boarded the yacht. Espo and several uniforms are on the way."

Viktor Salliger sighted. "We're… estranged."

Rikki and Castle looked suspicious, but said nothing. Kate's phone rang.

"Beckett."

"Bad news, Captain. We were too late," Esposito said. "He's cast off, and is running with no lights."

"I'll call 1PP and have them scramble a chopper. Good work finding the guy–now we just need to catch him."

* * *

Castle called Rita, and both mermaids arrived in time to see the operation unfold via live feed. They saw David Salliger caught in the search light beams and fire off several blasts from his carbine before fleeing below deck. The NYPD SWAT team rappelled down, took control of the yacht, and crawled through every nook, but didn't find anyone. They found one fewer set of SCUBA and a missing PPV, but knowing what happened didn't help the pursuit.

"In a normal situation, a pair of mermaids would get him easily," Rikki grumbled. "And we'd be glad to help."

"But he'd just paralyze you and take your rings," Castle said.

Rita seemed to think intensely. "What is it?"

"Maybe nothing, Captain–do what you can on land, and thank you. I don't even know if it'll work." With that, she left.

"Rikki?" Castle inquired.

"I don't have any ideas… sorry."

"I'll put out an APB on David Salliger, and have CSU take that boat apart. It doesn't seem like we can do anything to protect the mermaids, though."

That night, Kate had trouble going to sleep. Castle held her and tried to soothe, but these were weak distractions from the fact that there were victims she failed. So when the phone rang and ten past five in the morning, she snapped it up.

"Beckett."

"Morning, Captain," Vikram Singh greeted her. "I broke the _Cormorant_'s–that's the yacht's name–GPS encryption. We got her history of travel over the past six months. And there's an interesting place that shows up repeatedly.

"It's a beach house on Long Island with no link to Viktor or David Salliger."

"Send me the address," Kate said. "Good work. Come on, Castle."

* * *

Ryan and Esposito exited the house in fury. "No Salliger, but there were ten girls locked up, two to a room. No food or water for two days."

Two cars rolled up at that moment. A statuesque woman got out of one and headed straight for Kate. "Selena Rummel, New York State CPS," she flashed her badge. "May I see the victims?"

"Of course. I assume you know how to avoid contaminating a crime scene?"

Rummel smirked, pulled on a pair of latex gloves, and headed inside. "Don't worry," Rita Santos, who'd been in the other newly arrived car, told her. "She's a mermaid."

"What–you mean that ID is fake–"

"Oh, it's real," Santos said. "I just put her on alert so that she'd be the agent on the scene if the girls were found."

"You look happy."

"We should go inside, Detective."

"No one but the prisoners," the uniformed cop at the door informed them.

"I assumed that, not seeing anyone in handcuffs. I still want to see for myself."

They walked through the house, gave several glances in the rooms where the little mermaids were kept, and then Rita led them to the basement.

She flipped on the lights. "This place is not New York, but it's not wilderness," she began. "Salliger had to keep his hostages on land–unless he was here all the time, they would have escaped on the ocean. But he also had to bring them in, and he couldn't risk anyone noticing."

They looked about and eyes fell on a carpet sitting in the middle of the floor. It looked out of place on bare cement. Rikki leaned down and rolled the rug up. Underneath was a round metal door some four feet across.

"Mr. Castle," Rita said, and together she and the writer pulled the heavy lid away, revealing a pool of water. Kate knelt next to it and lowered her gloved hand inside before bringing it to her tongue. "Ocean water," she said. "So there's a channel here."

Rita nodded, then drew something from her pocket. "Are you ready, Detective?"

"Wait–he's in there?"

"Yes."

"He has a gun!" Castle shouted.

"Not anymore. You'll see."

"Castle, take my backup gun," Kate said.

He extracted it from her ankle holster and held it up. Then Kate looked at Rita and nodded.

The signal flare in her hand ignited with the familiar pinkish glow. Rita dropped the burning torch in the pool, but this fire didn't extinguish, instead lighting up the entire volume of water in an eery glow.

"That was a signal?"

Rita nodded.

"How long?"

"Not long."

As if on cue, a loud splash was followed by something being hurled out of the pool and onto the concrete floor the basement. "Don't move! NYPD!" Kate shouted, while Castle trained the gun on the man in a wetsuit with an oxygen tank on his back.

The mermaids carefully avoided getting splashed while Kate approached and cuffed the still dazed diver. Then she pulled off his mask.

"David Salliger, you are under arrest for murder and kidnapping."

He smiled. "All I have to do is talk about mermaids, and they'll declare me unfit to stand trial," he said.

"Have you considered the sort of justice we mermaids might serve should land peoples' fail?" Rita snapped. "By the time you find out, it'll be too late to change your mind."

Salliger gulped, and Kate and Castle hauled him up. "Let's go."

Four heads appeared in the pool. He glared back at them. "I don't understand. I still had power of the horn! Why didn't it work? It stuns mermaids!"

They laughed. One of them pulled up to sit on the edge of the pool, blue tail slapping on the surface. "Hmm…" he murmured in a distinctly masculine voice as he reached behind to unclasp the bikini and pull it off to reveal a flat, muscular chest. "How about because I'm not a mermaid?"


	5. Chapter 5

5

Two days later, once the paperwork from the case was done, the Castles invited Rita and her friends to their loft. After dinner, Rikki and Alexis engrossed themselves in conversation about oceanography, while Zac the Merman, his girlfriend Evie, and the other two mermaids who'd helped apprehend Salliger had hit off with Martha, excited for the opportunity to sample the New York theater scene. Rita and Selena remained with Kate and Rick.

"I want to thank you on behalf of the Atlantic Pods, Detective," Selena said. "I've arranged for the girls to be returned to their mothers, and they all can't thank you enough."

"It's my job–even if the ocean is out of my jurisdiction," she joked.

"So how long did it take to swim from Australia?"

Rita laughed. "It would have been five days, and I'd need to sleep for a week afterwards," she said. "That crew might pull it off," she waved at the young merpeople. "We flew in," she said. "Why?"

"Just curious."

"Castle…"

"You're going to put us in your books?" Selena demanded.

"Not you, specifically," he defended.

"Uh-huh. I've read Nikki Heat." She pointedly looked at Kate.

"I can't exactly follow a mermaid around and observe her daily routine," he said. "Besides, Nikki Heat and mermaids don't go well together. It'll be a new series, fantasy or sci-fi. Now that I know there are merpeople among my fans, I want them to remain fans."

Rita considered. "We're all thinking what might happen if the secret is broadly revealed," she opened. "I won't give you an answer right away."

"You might start a mermaid craze in literature, babe, the way Meyer did with vampires."

"Kate Castle!" he feigned offense. He then turned to Rita and Selena. "Please tell me vampires are real."

"Never thought so, but there'd be little opportunity for us to meet."

"Really, Castle? I don't want anyone to drink my husband's blood. Mermaids are plenty for now."

"Speaking of husbands, I better get home," Selena said. "It was good to meet you–Rita, Detective Beckett. Mr. Castle."

One by one, the guests left, until there were only Rikki and Rita left. Just before they were about to step out, Kate's eyes expanded with fear. "Wait!" she called out.

Castle instantly moved to her side. "What's wrong?" Rita asked.

"What happened to the horn? I don't want anything like this to happen again."

"You might not be fortunate enough to get Kate Beckett on your case next time." Kate smiled at him.

"Still," she said.

"I gave it to the matriarch of the Iceland Pod," Rikki said. "Three of the girls were from there, and I asked their mother to let me see her."

"Why them?" Even Rita seemed surprised.

"Because they live in a volcanic zone," she said. "They'll weigh it down and drop it into the lava. It's gone."

"Hmm…" Castle stroked his chin in thought.

"Idea for your novel?" Rita grumbled slightly.

"No. Fiction or not, I wouldn't write something to encourage real danger. But you _should_ consider the possibility. How was the horn originally made? Who might know or find that out? What might Salliger pass on? Are the alternatives for which there's no need to steal moon rings?"

Rita and Rikki exchanged a worried glance. Kate leaned into him.

"That's why I keep him around."

Rita sighed wistfully. "Thank you for everything, once again."

"Don't be strangers."

They said their goodbyes. When the door closed, Castle turned to his wife.

"Really? _That's_ why you keep me around?"

"The crazy theories? Among other things. Come on," she dragged him. "I want to see what else you're good for."

He lifted her off the floor and planted a kiss. "You weren't jealous about the mermaids, were you?"

"Well," she drawled, "like you said–can't follow them around and observe."

"Apparently, there's a pool that–"

"No," she growled. "You stick with me."

He stopped, cupped her face and tilted her head to meet her eyes.

"Always."


End file.
